gridsort.py

# this is just the third step 

input = [ 2, 8, 3, 5 ] # an array of unique items 
n = len(input)

# (...)

order = [ 3, 0, 2, 1 ] # first two steps created this

output = [ 0 ] * n
for i in range(n):
    output[order[i]] = input[i]

assert output == [8, 5, 3, 2]